1. Field of the Invention
The present invention relates to an X-Y stage apparatus provided with a moving table that can move within an XY plane, and which can position a component mounted on top of the moving table within the XY plane.
2. Description of the Related Art
In the past, this type of X-Y stage apparatus has been used in many industrial fields, such as mounting apparatuses of electronic components (chip mounter) machine tools, and controlling mechanism of optical systems (lens, mirrors, and others).
FIG. 15 shows a conventional X-Y stage apparatus 900. This X-Y stage apparatus 900 has a Y-axis guiding mechanism 906 with an X-Y table 907, mounted on top of an X-axis table (not shown) of an X-axis guiding mechanism 903. The X-axis guiding mechanism 903 is provided with an X-axis ball screw 902 arranged in an X-axis direction, and an X-axis servomotor 901 that rotates and drives this X-axis ball screw 902. The whole Y-axis guiding mechanism 906 is moved and positioned in the X-axis direction by controlling this X-axis servomotor 901, as appropriate. The Y-axis guiding mechanism 906 is provided with a Y-axis ball screw 905 arranged in a Y-axis direction, and a Y-axis servomotor 904 that rotates and drives this Y-axis ball screw 905. The X-Y table 907 is moved and positioned in the Y-axis direction by controlling this Y-axis servomotor 904, as appropriate. Therefore, the location of the X-Y table 907 can be positioned in the X-axis and Y-axis directions by controlling the X-axis and Y-axis servomotors 901 and 904.
For controlling methods of the X-axis and Y-axis servomotors 901 and 904, there is for example, a semi-closed-loop control method that surmises the amount of movement of the X-Y table 907 from the rotating amount of the X-axis and Y-axis ball screws 902 and 905, which is measured by encoders, and controls the X-axis and Y-axis servomotors 901 and 904 with these surmised values. There is also a fully-closed-loop control method that directly measures the amount of movement of the X-Y table 907 with a linear gauge or the like, and feedback controls the X-axis and Y-axis servomotors 901 and 904 with these values.
In recent years, the demand for xe2x80x9chigh-speed controlxe2x80x9d and xe2x80x9cprecision controlxe2x80x9d of an X-Y table 907 has been enhanced, corresponding with the advancement in technology. When trying to accomplish high-speed control, there was a limit in making the control speed faster with a driving method using a shaft mechanism with ball screws 902 and 905, because vibration increased, for example, when changing between normal rotation and reverse rotation, or when accelerating or decelerating rapidly. When trying to accomplish precision control with the semi-closed-loop control method, it was difficult to control the X-Y table 907 with precision, because there were no considerations for a bending of each of the ball screws 902 and 905, or for backlashes, or the like.
It was possible to achieve a more precise control with the fully-closed-loop control method, but the position measuring signals of the X-Y table 907 became unstable, because the vibration of each of the ball screws 902 and 905 was transmitted to the X-Y table 907, when the controlling speed went up. As a result, there was a problem that the responsiveness of the feedback control could not be enhanced, what with the signal becoming unstable.
Furthermore, since the X-Y stage apparatus 900 had a two-tiered construction, with the Y-axis guiding mechanism 906 mounted on top of the X-axis guiding mechanism 903, the center of gravity was high, and an overturning moment was prone to be generated. As a result, positioning error increased because a swing of the X-Y table 907 was generated, when controlling a rapid acceleration or deceleration. In the case of such two-tiered construction, the whole Y-axis guiding mechanism 906 becomes a moving load (inertia-load) for the X-axis guiding mechanism 903 located at the bottom tier, but only the X-Y table 907 becomes the moving load for the Y-axis guiding mechanism 906. Hence, there was a difference in the responsiveness of control in the X-axis direction, and the control in the Y-axis direction. When driving the X-Y table 907 in both of the X-axis and the Y-axis directions at the same time, as in drawing a circle, or moving in a diagonal direction of the X-Y axes, for example, there arose a problem that precision deteriorated, and it was difficult to realize high-speed control.
The present invention was made in view of the above-mentioned problems, and it is an object of this invention to achieve an X-Y stage apparatus compact in constitution, and which can control with high-speed, and with high-precision.
This invention achieves the above-mentioned objects by providing an X-Y stage apparatus comprising a stationary base, and a moving table that can be displaced within an XY plane relative to the stationary base, provided that an X-axis, a Y-axis, and a Z-axis are at right angles to each other. The X-Y stage apparatus is provided with a plurality of elastic hinges of one or more types, which have flexible characteristics only in one or two directions among the X-axis, Y-axis, and Z-axis directions, and rigid characteristics in the other directions. The elastic hinges are arranged along one direction among the X-axis, Y-axis, and Z-axis directions, and allows relative displacement between members connected to both sides of the hinges only in the flexible direction. The moving table is supported within the XY plane relative to the stationary base with slight displacement made possible by utilizing an elastic deformation of each of the elastic hinges in the aforementioned flexible direction. Moreover, the X-Y stage apparatus is provided with an X-axis linear motor which has a stator portion and a moving portion arranged on the stationary base and the moving table, respectively, and which can move the moving table in the X-axis direction, relative to the stationary base. The X-Y stage apparatus is also provided with a Y-axis linear motor which has a stator portion and a moving portion arranged on the stationary base and the moving table, respectively, and which can move the moving table in the Y-axis direction relative to the stationary base. In this constitution, the moving table is displaced slightly within the XY plane relative to the stationary base by the X-axis and Y-axis linear motors.
In this X-Y stage apparatus, the inventor of this invention adopted a constitution provided with an xe2x80x9celastic hingexe2x80x9d that supports the moving table in a movable state in the X-Y axis direction, and a xe2x80x9clinear motorxe2x80x9d that drives the moving table.
The basic construction of the elastic hinge itself is publicly known, and in general, has characteristics being flexible only in one particular direction and rigid in the other directions, and has a function that allows relative displacement only in the aforementioned flexible direction between members connected to both sides thereof. Assume the case of an elastic hinge having flexible characteristics only in the X-axis direction and rigid characteristics in the Y-axis and Z-axis directions, and which allows relative displacement only in the X-axis direction between members connected to both sides thereof, when it is arranged along the Y-axis direction in the XY plane. In this case, for example, it is possible to move a movable member in the X-axis direction relative to a fixed-member with the elastic deformation of the elastic hinge. On the other hand, this elastic hinge hardly allows a relative movement in the Y-axis and Z-axis directions. In other words, the elastic hinge is made so that it can xe2x80x9cguidexe2x80x9d the movable member in the X-axis direction.
Furthermore, for example, when a rod-formed elastic hinge that has characteristics of being flexible in the bending direction and rigid in the axial direction is arranged with its axis coinciding with the Z-axis direction, a relative displacement within the XY plane between members connected to both sides of the hinge can be allowed.
When the moving table is made to be supported in a movable state within the XY plane utilizing such elastic hinges, it is possible to make it more compact, and with low cost, because complicated guiding mechanisms such as in conventional methods become unnecessary. It is also possible to make the inertia load of driving means that drives the moving table smaller, and achieve a drive control with good responsiveness and high precision, because the construction of members around the moving table (members that are driven with the moving table) can be made simple.
In this invention, the moving table supported through the intervention of such elastic hinges is made to be driven by a linear motor. This is because the following xe2x80x9csynergy effectsxe2x80x9d can be achieved by combining these.
The linear motor adopted as a driving apparatus in this invention has a stator and a movable element installed directly between the stationary base and the moving table, and has characteristics in which it can directly drive a relative member with the thrust of the magnetic force in xe2x80x9cnon-contact statexe2x80x9d, and this enables to achieve a high-speed and high-precision control. Therefore, it is possible to drive the moving table in one direction (the X-axis direction, for example), and also xe2x80x9callowxe2x80x9d a movement of the moving table in an orthogonal direction to that direction (the Y-axis direction, for example), because the linear motor is a non-contact type. The inertia load is significantly reduced, and it is possible to lower the center of gravity, because there is no need to mount a Y-axis-direction driving apparatus on top of an X-axis-direction driving apparatus, as in the driving-mechanisms such as a ball screw.
There is of course a possibility of an xe2x80x9cslight deviation (slide component)xe2x80x9d generating in displacing the moving table, because a change in the longitudinal dimension of the elastic hinge is prone to occur, when the elastic hinge is elastically deformed. But this deviation can be tolerated in linear motors, and the margin of error of this xe2x80x9cdeviationxe2x80x9d can be compensated by the control of the linear motor if necessary.
Therefore, an,extremely high-speed and high-precision positioning within the XY plane is made possible, because the elastic hinges and the linear motors are combined under a rational philosophy.
This elastic hinge is also characterized in that the reaction force (restoring force) generated corresponding to the displacement of the moving table has xe2x80x9clinearityxe2x80x9d (or characteristic close to linearity). Generally, the amount of displacement of the moving table can be calculated easily from the amount of rotation or the like when using mechanical driving means such as ball screws. However, with linear-motors that drive with magnetic force, a fully-closed-loop control is usually adopted, which controls by directly measuring the amount of displacement of the moving table. Therefore, when there is a big non-linear movement in the guiding mechanism, the control tend to be complicated and affects the responsiveness, or the like. However, since it has been constituted to have characteristics which is nearly equal to linearity, as mentioned above, it has become easy to control with the feedback of the X-axis and Y-axis direction measurement values of the moving table, and a high-speed and high-precision positioning (position compensation) has become possible.
As a result, a positioning control with an excellent responsiveness is available, when the driving forces of the respective linear motors and the above-mentioned restoring forces are combined rationally. If necessary, it is possible to slightly vibrate or oscillate-and-rotate components arranged and installed on top of the moving table (these movements can be conceived as a high-speed and cyclic positioning control). This is a result of a fusion between the characteristics of the linear motors being capable of changing the direction of the thrust force between normal and reverse at high-speed (electrically), and the characteristics of the restoring force being xe2x80x9clinearxe2x80x9d.
When trying to conduct such slight and precise control with the intervention of ball screws or bearings, for example, there was a problem in that a repeated stress was affected upon a limited portion (particular portion) of these ball screws or the like, and fatigue was generated upon this limited portion to lower the lifespan. However with this elastic hinge, it is possible to exert stable controlling characteristics for a long period of time, because rolling fatigue does not generate in this elastic hinge, structurally.
It is also possible, if necessary, to omit an action (control) to return the moving table to a neutral position, because the moving table tries to automatically return to the neutral position with the restoring force of the elastic hinge, when each of the linear motors have their power turn off, for example. This is because a non-contact type linear motor becomes free in relation to the moving table, when the power of the linear motor is turned off and the thrust force is freed. This is different from the mechanical types such as the ball screw, or the like.
There is no particular limit in the number or shape of the above-mentioned intermediate member or elastic hinge. These can be arranged as appropriate, corresponding to necessity. For example, the following constitution can be adopted. In this constitution, there are provided a plurality of first elastic hinges that has flexible characteristics only in the X-axis direction, and rigid characteristics in the Y-axis and Z-axis directions, and allows relative displacement only in the X-axis direction between members connected to both ends of the first elastic hinge by being arranged along the Y-axis direction within the aforementioned XY plane. Also provided are a plurality of second elastic hinges that has flexible characteristics only in the Y-axis direction, and rigid characteristics in the X-axis and Z-axis directions, and allows relative displacement only in the Y-axis direction between members connected to both ends of the second elastic hinge by being arranged along the X-axis direction within the aforementioned XY plane. In this constitution, the stationary base, the intermediate member, and the moving table are connected with each other by combined use of the first and the second elastic hinges in such a manner that the moving table to be displaced slightly and the stationary base are arranged at a location including the XY plane, and the intermediate member is interposed within the aforementioned XY plane in-between the stationary base and the moving table, so that the moving table is slightly movable within the XY plane relative to the stationary base, and supported at a prescribed location with regard to the Z-axis direction.
When the intermediate member is interposed between the stationary base and the moving table within the XY plane, and all three of them are linked together through the intervention of the first and second elastic hinges, it becomes possible for the moving table to be xe2x80x9cguidedxe2x80x9d and moved linearly in both the X-axis and the Y-axis directions relative to the stationary base, because the intermediate member comes to maintain a fixed state with regard to the direction in which the first and second elastic hinges are made rigid. Thereby, a control with excellent responsiveness and stability can be achieved, because there is intrinsically no backlash, slips or roll.
In this case, it may be constituted as follows: the intermediate member is formed into a rectangular ring-shape having two extended portion in the X-axis direction, and two extended portion in the Y-axis direction; provision of the plurality of the first elastic hinges arranged in the Y-axis direction between the two extended portion in the X-axis direction of the intermediate member and the stationary base allows the relative displacement between the stationary base and the intermediate member in the X-axis direction; provision of the plurality of the second elastic hinges arranged in the X-axis direction between the two extended portion in the Y-axis direction of the intermediate member and the moving table allows the relative displacement between the intermediate member and the moving table in the Y-axis direction. This constitution is easy to design because the construction is simple, and it is possible to easily arrange each of the elastic hinges in a line symmetrical manner with regard to the X-axis and Y-axis directions, because elastic hinges are arranged and installed on each of the total of four extended portions (that is, on each of the sides of the ring). As a result, it is possible to suppress an occurrence of a phenomenon in which the intermediate member itself rotates around the Z-axis. Hence, a positioning with high precision is possible.
By constituting the intermediate member in such a ring-shape, the rigidity of the intermediate member itself is increased also, suppressing an elastic deformation of the intermediate member itself, and the precision of the positioning is improved.
However, in this invention, the constitution of the intermediate member is not limited to the above-mentioned constitution. The following constitution can be adopted for the intermediate member other than the constitution of forming it into a rectangular ring-shape. Namely, for example, the intermediate member is divided into a plurality of intermediate members including a first intermediate member and a second intermediate member. In this constitution, the relative displacement of the moving table in the X-axis and Y-axis directions relative to the stationary base is allowed by arranging the first elastic hinge between the stationary base and the first intermediate member to allow the relative displacement between both members in the X-axis direction, and by arranging the second elastic hinge between the first intermediate member and the moving table to allow the relative displacement between both members in the Y-axis direction. On the other hand, the displacement of the moving table in the X-axis and Y-axis directions relative to the stationary base is allowed by arranging the second elastic hinge between the stationary base and the second intermediate member to allow the relative displacement between both members in the Y-axis direction, and by arranging the first elastic hinge between the second intermediate member and the moving table to allow the relative displacement between both members in the X-axis direction.
In this case, the divided first and second intermediate members, including the aforementioned first elastic hinges and the second elastic hinges linked together to the first and second intermediate members, should be arranged so that they are point-symmetric with regard to the center of the moving table.
For example, when the above-mentioned ring-shaped construction is adopted as the construction for the intermediate member, the inertia load in one of the directions is almost equal to xe2x80x9cmoving table+ring-shaped intermediate memberxe2x80x9d, whereas the inertia load in the other direction is almost equal to only the xe2x80x9cmoving tablexe2x80x9d. Therefore, it is inevitable that the inertia load in the X-axis and Y-axis directions differ to some extent (although with much less effects compared to constructions using conventional guide mechanisms).
However, it is possible to make the inertia load in the X-axis and Y-axis directions uniform, by dividing the intermediate member, and arranging the first elastic hinges and the second elastic hinges so that they are point-symmetric with regard to the center of the moving table, for example. By doing so, it is possible to have a positioning control balanced in both directions.
In other words, in this constitution having the intermediate member divided, the elastic deformation of the first elastic hinge of each of the first and second intermediate members in the X-axis direction contributes to the relative movement of the moving table in the X-axis direction to the stationary base. Also, the elastic deformation of the second elastic hinge of each of the first and second intermediate members in the Y-axis direction contributes to the relative movement of the moving table in the Y-axis direction to the stationary base. Therefore, when driving the moving table in the X-axis direction, the inertia load will become approximately xe2x80x9cmoving table+first intermediate memberxe2x80x9d (ignoring the components mounted on the moving table), and when moving the moving table in the Y-axis direction, the inertia load will become approximately xe2x80x9cmoving table+second intermediate memberxe2x80x9d. As a result, it is possible to make the inertia load in the X-axis and Y-axis directions uniform, by making the number of the first intermediate members and the second intermediate members the same, or making their weights equal, for example. By doing so, it is possible to have a balanced positioning control in both of the directions.
This point-symmetric support cannot be implemented with a construction provided with a single intermediate member. It can be achieved only with a constitution that has the intermediate member divided into a plurality of intermediate members, and in which both the first and second elastic hinges exist between the stationary base and the plurality of intermediate members, and both the first and second elastic hinges exist between the plurality of intermediate members and the moving table.
In the above constitution, the elastic hinges were limited to being arranged in the X-axis or Y-axis direction. However, as apparent from the above-mentioned view, the compatibility between the xe2x80x9celastic hingexe2x80x9d and the xe2x80x9clinear motorxe2x80x9d is extremely good, and similar effects are possible with the following constitution.
This invention achieves the above-mentioned objects by providing an X-Y stage apparatus comprising a stationary base, and a moving table that can be displaced within an XY plane relative to the stationary base, provided that an X-axis, a Y-axis, and a Z-axis are at right angles to each other. The stationary base is arranged with a prescribed clearance spaced in the Z-axis direction with regard to the moving table. The X-Y stage apparatus is provided with at least three elastic hinges in the Z-axis direction that has rigid characteristics only in its longitudinal direction, and which is arranged and interposed in the clearance along the Z-axis direction, and which slightly displaces the moving table in the XY plane relative to the stationary base by elastic deformation of the hinges. Moreover, the X-Y stage apparatus is provided with an X-axis linear motor which has a stator portion and a moving portion arranged on the stationary base and the moving table, respectively, and which can move the moving table in the X-axis direction, relative to the stationary base. The X-Y stage apparatus is also provided with a Y-axis linear motor which has a stator portion and a moving portion arranged on the stationary base and the moving table, respectively, and which can move the moving table in the Y-axis direction relative to the stationary base. In this constitution, the moving table is displaced slightly within the XY plane relative to the stationary base by the X-axis and Y-axis linear motors.
In this X-Y stage apparatus, a constitution is adopted in which the moving table is, supported by elastic hinges in the Z-axis direction. This constitution has each of the elastic hinges elastically deformable in both the X-axis and Y-axis directions, and moves the moving table within the XY plane relative to the stationary base.
This kind of elastic hinge in the Z-axis direction cannot guide the moving table xe2x80x9clinearlyxe2x80x9d in the X-axis or Y-axis direction, structurally. However in this case, the X-axis and Y-axis linear motors are used as the drive source, which can produce a linear thrust force. Therefore, an effective control is possible in combination with the elastic hinges in the Z-axis direction, because each of the linear motors can also serve as a xe2x80x9cnon-contact linear guide.xe2x80x9d In other words, each of the linear motors serves as a xe2x80x9cdriverxe2x80x9d, and also as a xe2x80x9cguide (regulator).xe2x80x9d
As a result, it is possible to position the movement of the moving table in the XY plane with high speed and high precision by using the X-axis and Y-axis linear motors. It is also possible to reduce manufacturing cost due to its simple constitution with the elastic hinges in the Z-axis direction supporting the moving table.
It is preferred that three elastic hinges are installed, so that they are positioned at the corresponding positions with the respective apex locations of a virtual equilateral triangle within the XY plane, whose center of the gravity coincides with the center of the gravity of the moving table.
There is no particular limitation in the number of the X-axis and Y-axis linear motors. For example, when two X-axis linear motors are arranged and installed with a prescribed interval in the Y-axis direction, a correction of the location in the Z-axis rotating direction is made possible by the difference in the amount of displacement of each of the two linear motors. The Y-axis linear motor can be arranged and installed similarly, as a matter of course. It is also possible to arrange three or more linear motors in each of the directions.
In this invention, there is no particular limitation in the specific constitution of the elastic hinge. However, the following constitution is conceivable for an elastic hinge that reduces stress concentration to a minimum.
That is, a constitution provided with a bridge member connecting the two members, and having an easily deformable reduced-thickness portion formed by forming notches at a plurality of positions separated in a longitudinal direction of the bridge member on an outer circumference surface of the bridge member, in which the depth of the notch in a radius direction of the bridge member is configured to be smaller than half of L, L being the length of the notch in an axial direction of the bridge member.
In this regard, the depth of the notch F1 was configured to be exactly half of L1 (in a concept of comparing with this invention), where L1 was the length of the notch, because the shape of the notch was made a xe2x80x9csemicirclexe2x80x9d, in conventional elastic hinges.
In contrast, when suppressing the depth of the notch to be smaller than half the length of the notch, the generated maximum stress can be reduced in comparison to conventional elastic hinges.
Various specific constitutions can be conceived, to configure the depth smaller than half the length of the notch L.
For example, the notch can be formed to provide a notched cross section with an outline of a circular-arc smaller than a semicircle.
Alternatively, the notch can be formed to provide a notched cross section with an outline of an ellipse-arc.
By doing so, it is possible to ease the concentration of stress, and reduce maximum stress, because the curve of the notch can be made milder.
When a parallel portion, with unchanged cross section for a prescribed length in the longitudinal direction of the notch, is provided in the minimum cross section portion at the center of the longitudinal direction of the notch, the thinnest portion of the reduced thickness portion can be made to be broader than conventional ones. In other words, the portion that receives stress can be made a plane, as opposed to the line portion in conventional hinges. Consequently, the stress can be dispersed to a broad range, and the maximum stress exerted upon the elastic hinge can be reduced.
In this case, when the bridge member is formed to have a rectangular cross section, and the notches are formed symmetrically on two opposing outer side faces facing towards the bending and deforming direction, the thinning is done only in one direction. Hence, it becomes easy to bend only in the direction that had the portion thinned, and maintains a state in which it is difficult to bend in the other directions. Therefore, an elastic hinge with bending directionality is realized. In particular, a balanced bending deformation can be achieved due to the reduced thickness portion located at the center portion in the thickness direction of the bridge member by providing symmetrical notches arranged on two outer side faces.
It is also possible to form the bridge member to have a circular cross section, and have the notch formed in annular form around the whole circumference of the bridge member. In this constitution, an elastic hinge is realized, which is easy to bend in all directions, with no bending directionality.